Venoms are complex mixtures of biologically active components. The effect of a venom on a mammal is due to the interaction of these venom components with normal body processes. To understand how a venom causes problems, the venom must be fractionated and its toxic components identified, isolated, and characterized. Only after this knowledge is available can specific treatment of envenomation be accomplished. Also, purified venom components can be very useful. The four venoms which are being studied in this project are those obtained from the timber rattlesnake, Crotalus horridus horridus, the eastern cottonmouth, Agkistrodon piscivorus piscivorus, the northern copperhead, Agkistrodon contortrix mokasen, and the brown recluse spider, Loxosceles reclusa. All four of these venoms produce severe local tissue responses while the systemic effects of the snake venoms are comparatively mild. Four hemmorrhage-inducing components have been identified in timber rattlesnake venom. These components will be purified and characterized. An apparently neurotoxic basic protein which has been purified from the timber rattlesnake venom will also be characterized. An improved method for purifying the toxic components from brown recluse spider venom will be developed. The venoms of the eastern cottonmouth and the northern copperhead will be fractionated and their toxic components identified.